1. Field of the Invention
The present invention relates to a liquid-discharge-head substrate, a method of manufacturing the liquid-discharge-head substrate, and a liquid discharge head.
2. Description of the Related Art
A typical thermal type liquid discharge head (hereinafter, also referred to as head) includes a liquid-discharge-head substrate (hereinafter, also referred to as head substrate) having a liquid discharge heater and a conductive layer for electrical connection, and a member having a discharge port which corresponds to the heater and discharges liquid.
In recent years, functions for stabilizing discharge of liquid are added to a head substrate. One of the functions is obtained by a technique of pre-heating the head substrate by a heating member (hereinafter, also referred to as sub-heater) provided at the substrate, in addition to a heating element for liquid discharge (hereinafter, also referred to as heater).
As such a sub-heater, for example, Japanese Patent Laid-Open No. 3-005151 discloses a structure in which a heater and a sub-heater are formed of a conductive layer. The sub-heater heats a head substrate to prevent a discharge characteristic from being degraded at a low temperature.
Meanwhile, a head substrate increases in size as the number of heating elements increases. Also, when the number of colors of inks increases, the number of supply ports increases, resulting in the size of the head substrate increasing. Hence, in related art, variation in temperature distribution may likely appear in the head substrate when the head substrate is pre-heated.
When the variation in temperature distribution in the head substrate increases, discharge characteristics such as a discharge amount and a discharge speed of ink droplets may vary among a plurality of nozzles. This may cause density unevenness and disorder of landing points of the ink droplets. Recording quality may be degraded.
In particular, when pre-heating is performed before a recording operation, the temperature of the head substrate has to be quickly increased to a predetermined temperature. Owing to this, power to be applied to the sub-heater is increased. A large temperature gradient may appear in the head substrate between a position close to the sub-heater and a position far from the sub-heater.
In addition, when pre-heating is performed to keep the temperature of the head at a predetermined temperature during a recording operation, a temperature gradient may increase as the temperature of the head substrate is set high. This may degrade recording quality.